Chamber Sentry is a rare Artifact Creature — Construct card from Jumpstart (JMP), collector number 461. Current market price: $0.16, TCGplayer market prices via Scryfall.
This creature enters with a +1/+1 counter on it for each color of mana spent to cast it. {X}, {T}, Remove X +1/+1 counters from this creature: It deals X damage to any target. {W}{U}{B}{R}{G}: Return this card from your graveyard to your hand.